What is a reasonable blood pH cutoff for Intensive Care Unit (ICU) admission?

From the Guidelines

A reasonable blood pH cutoff for ICU admission is generally considered to be below 7.30, as indicated by the European Respiratory Society guidelines 1. This cutoff is based on the presence of severe acidosis, which can lead to hemodynamic instability, cardiac dysfunction, and altered mental status. However, the decision for ICU admission should not be based solely on pH but should consider the patient's overall clinical status, the rate of pH change, underlying cause, response to initial treatments, and presence of other organ dysfunction. For example, a patient with diabetic ketoacidosis with a pH of 7.15 may require ICU admission for close monitoring and insulin infusion, while a patient with chronic respiratory acidosis with a stable pH of 7.30 might be managed in a regular ward. The trend in pH values over time is often more important than a single measurement, as rapidly worsening acidosis or alkalosis indicates a more urgent need for intensive care, as supported by the BTS guideline for oxygen use in adults in healthcare and emergency settings 1 and the official ERS/ATS clinical practice guidelines for noninvasive ventilation for acute respiratory failure 1. Additionally, the BTS/ICS guideline for the ventilatory management of acute hypercapnic respiratory failure in adults suggests that a pH <7.25 can be used as a threshold for considering provision of invasive mechanical ventilation 1. Key factors to consider in ICU admission decisions include:

• Severity of acidosis or alkalosis
• Rate of pH change
• Underlying cause of the pH imbalance
• Presence of other organ dysfunction
• Response to initial treatments.

From the Research

Blood pH Cutoff for ICU Admission

The decision to admit a patient to the Intensive Care Unit (ICU) based on blood pH levels is complex and depends on various factors, including the underlying cause of the acidosis and the patient's overall clinical condition.

• The normal blood pH range is between 7.35 and 7.45 2, 3.
• A blood pH below 7.20 is generally considered indicative of severe acidosis, which may require ICU admission 4.
• However, the use of sodium bicarbonate to correct acidosis is controversial, and its effectiveness in improving clinical outcomes is not well established 2, 3, 4, 5, 6.
• A study published in 2018 found that sodium bicarbonate infusion did not improve clinical outcomes in patients with severe metabolic acidaemia, except in those with acute kidney injury 4.
• Another study published in 2021 found that early administration of sodium bicarbonate was associated with a lower odds ratio for ICU mortality in patients with vasopressor dependency, but the results were not statistically significant 5.

Considerations for ICU Admission

When considering ICU admission based on blood pH levels, the following factors should be taken into account:

• The severity of the acidosis, as indicated by the blood pH level and the presence of any underlying conditions that may be contributing to the acidosis 3, 4.
• The patient's overall clinical condition, including the presence of any organ dysfunction or failure 3, 4.
• The potential benefits and risks of sodium bicarbonate therapy, including the risk of metabolic alkalosis, hypernatraemia, and hypocalcaemia 4, 5.

Blood pH Thresholds

While there is no universally accepted blood pH threshold for ICU admission, the following thresholds may be considered:

• A blood pH below 7.20 may indicate severe acidosis and require ICU admission 4.
• A blood pH below 7.10 may indicate life-threatening acidosis and require immediate ICU admission 3.